The present invention relates to an improved lubricating fluid and particularly concerns an additive for such a fluid that will improve its seal swelling properties without at the same time imparting any detrimental effects thereto. The invention is also directed to additive concentrate packages that are intended for formulation into mineral oil base stocks to provide transmission fluids of improved seal swelling characteristics thereby enhancing fluid retention. These transmission fluids have utility as a lubricant for rotary engines.
A very high percentage of vehicles such as automobiles, tractors and earthmovers are now equipped with some type of semi-automatic or fully automatic transmission. These transmissions must be provided with a supply of fluid that serves the multiple functions of a power transmitting medium, a hydraulic control fluid, a heat transfer medium, and a satisfactory lubricant. A transmission fluid to be useful must be capable of operating over a wide temperature range, possess a high degree of oxidation resistance, be free of corrosive action, have foam control, have satisfactory low temperature fluidity, retain a useful viscosity at high temperatures, have transmission seal compatibility and lubricity without "stick-slip" of the transmission parts.
Exemplary of automatic transmission fluids are those disclosed in U.S. patents: U.S. Pat. No. 3,410,801 which is directed to a class of modifiers of the friction characteristics of automatic transmission fluids (hereinafter designated ATF) to reduce squawk and chatter of the transmission; U.S. Pat. No. 3,446,737 which is directed to an alternative class of friction modifiers for ATF, i.e. to reaction products of C.sub.50 to C.sub.250 carboxylic acids with amines: U.S. Pat. No. 3,451,930 which is directed to the high stress additives for ATF; and U.S. Pat. No. 3,309,967 which is directed to a further class of friction modifiers for ATF, i.e. the dialkyl esters of dimers of ethylene monocarboxylic aliphatic acids.
The current approach to improving ATF is to adjust and modify the various additives so as to extend their useful life time. This approach is of little value unless the fluid is retained within the transmission system. Many of the automatic transmission in use in vehicles at the present time are losing significant quantities for automatic transmission fluid, principally because of deterioration of the rubber-type seals or gaskets. As a result of this there have been numerous attempts to develop oil-soluble additives that can be formulated with or added to the ATF automatic transmission to swell and soften the rubber in those seals and gaskets and thereby enhance retention. The seal swell-soften additive should not lower the viscosity of the automatic transmission fluid nor impair its oxidation stability. Further, the additive preferably should be biodegradable and not have adverse toxicological properties. The essential need is to improve the ATF originally placed in transmissions so that it is more completely and longer retained.
U.S. Pat. No. 3,389,088 teaches one class of additives which performs to suitably swell the various gaskets and seals of the automatic transmission system. This class is aliphatic alcohols of 8 to 13 carbon atoms, e.g. tridecyl alcohol.